Contemporary and future aerospace vehicle structural requirements appear to find advantageous features in the recent advances in filamentary composite materials. Structural designs utilizing composite materials to exploit the unidirectional nature thereof appear promising in aerospace structural components. Relatively thin resin preimpregnated carbon, graphite and other fiber tapes are commercially available wherein the fibers are parallel monofilaments that extend the length of the tape. Thin laminates of these tapes have been utilized heretofore but efforts to cure thick laminate sections have been difficult and have resulted in low quality of uneven physical property characteristics due to the entrapment of air or polymer by-products within the laminate caused by premature cure of the outer perimeter areas that close off the venting paths of the by-products and air. This has also caused density variation through the laminates since, as the thicker laminate warms and becomes viscous, the laminating pressures usually cause more resin flow or movement than desired to thereby create a washing effect or disorientation of the fibers and a resulting reduction of the directional strength. Further, as these prior art attempts to form thick laminates were cured, the chemical reactions of the polymer created heat via exothermic reactions faster than the surrounding surface could dissipate it. This caused the polymer to boil off by-products faster than they could escape with a corresponding temperature increase accelerating the cure and trapping bubbles in the laminate.
There is therefore a definite need in the art for a process to prepare relatively thick laminate sections of composite materials for use in aerospace vehicle structures.
Accordingly, it is an object of the present invention to provide a new and unobvious process for laminating and curing relatively thick sections of resin preimpregnated fiber tape.
Another object of the present invention is a process for making laminate composite structural elements having controlled orientation of the monofilament fibers in the laminates.
A further object of the present invention is a process to produce void free thick composite laminates.
An additional object of the present invention is a process for securing partially cured composite laminates together to form a unitary structure.